Catalyst and reverse disproportionation process

ABSTRACT

A catalyst containing tungsten, antimony and an alkali or alkaline earth component on a support, preferably silica gel, is disclosed which is useful in reverse disproportionation of stilbene and ethylene to produce styrene.

This is a division of application Ser. No. 403,254, filed July 29, 1982now U.S. Pat. No. 4,419,526.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a catalyst and process for reversedisproportionation of ethylene and stilbene to produce styrene. Thecatalyst comprises tungsten, antimony and an alkali or alkaline earthcomponent on a support, preferably silica gel.

2. Description of the Prior Art

The production of styrene from stilbene and ethylene is disclosed inU.S. Pat. No. 3,965,206, the teachings of which are incorporated byreference. Use of conventional disproportionation catalysts such ascobalt molybdate on alumina, or tungsten oxide or silica, alumina orsilica-alumina, for reverse disproportionation is taught.

U.S. Pat. No. 3,764,635, Fattore, et al, the teachings of which areincorporated by reference, teaches a process for disproportionatingolefins using a catalyst of tungsten and bismuth on a support,preferably silica. The catalyst is active for disproportionation withoutany activation step.

U.S. Pat. No. 3,792,107, Fattore, et al, the teachings of which areincorporated by reference, discloses use of a catalyst of tungsten andcopper or tungsten and Group VIII metals, preferably Fe, Co or Ni, onsilica or other support. It is claimed that this catalyst requires noactivation before use in disproportionation.

U.S. Pat. No.3,728,414, Helden, et al, the teachings of which areincorporated by reference, teaches a conventional olefindisproportionation catalyst with a promoter, a Group IIIa metal on analumina carrier. Conventional olefin disproportionation catalysts aresaid to contain titanium, vanadium, chromium, manganese, zirconium,niobium, molybdenum, technetium, ruthenium, rhodium, palladium, tin,hafnium, tantalum, tungsten, rhenium, osmium, and iridium. Thisreference teaches that additional components, e.g., coactivators,hydrogenating components, components for isomerization of the doublebond, and the like may also be added. Coactivators listed include cobaltoxide, and compounds of iron, nickel, and bismuth.

U.S. Pat. No. 4,192,961 teaches conversion of a mixture of dibenzyl andstilbene with ethylene in the presence of a catalyst of chromium oxide,tungsten oxide, an oxide of an alkali metal and silica or alumisilicate.Styrene yields of 78 to 80 wt %, based upon conversion of ethylbenzene,dibenzyl and stilbene, are claimed.

U.S. Pat. No. 3,658,930, Kenton, et al, the teachings of which areincorporated by reference, teaches disproportionation of olefins using arhodium oxide promoter on conventional olefin disproportionationcatalyst, e.g., tungsten, molybdenum, rhenium, or tellurium on silica.

U.K. Patent Specification No. 1,205,677 teaches disproportionation ofolefins using a conventional catalyst, such as molybdenum trioxide,tungsten trioxide or rhenium heptoxide on alumina, silica, oralumina-silica and incorporating into this conventional catalyst asecond component to effect double bond isomerization of olefins. GroupVIII noble metals are suggested as being suitable, with preferredisomerization catalysts containing platinum and especially palladium. Analkali or alkaline earth metal ions are added to the catalyst to serveas a base to inhibit the oligomerization of branch chained olefins.

None of these prior art catalysts are believed to possess sufficientactivity and stability to permit their use in a commercial reversedisproportionation process.

Another failing of most prior art catalysts is that a relatively hightemperature activation procedure is necessary before the catalysts aresuitable for use. These catalysts are extremely active, but have veryshort lives before carbon and coke deposition destroys catalyticactivity. Frequent regeneration and activation of the catalyst arenecessary for a successful commercial process. It is desirable tominimize stress on the catalyst, and on the equipment by eliminatinglarge temperature swings necessary for activation and regeneration ofthe catalyst. It is also desirable if the catalyst has great stability,and is able to operate for relatively long periods.

SUMMARY OF THE INVENTION

The present invention provides a catalyst comprisingcatalytically-effective amounts of antimony, tungsten and an alkali oralkaline earth component on a carrier material.

In another embodiment, the present invention provides a process for thereverse disproportionation of stilbene and ethylene which comprisescontacting stilbene and ethylene at reverse disproportionationconditions with an activated catalyst containing catalytically-effectiveamounts of antimony, tungsten, and an alkali or alkaline earth componentor compounds thereof supported on a carrier material to produce styrene.

In a more limited embodiment, the present invention provides a processfor the reverse disproportionation of stilbene and ethylene into styrenecomprising contacting the stilbene and ethylene at a temperature of 300to 600 C. with an activated catalyst comprising tungsten, antimony, andan alkali or alkaline earth metal component or compound thereof onsilica gel carrier, and wherein the atomic ratio of antimony to tungstenis from 1:20 to 1:1, to produce styrene, and continuing said contactuntil said catalyst has been at least partially deactivated by cokedeposition, removing said deactivated catalyst from contact withreactants and regenerating said catalyst by oxidizing coke from saidcatalyst with an oxygen containing gas to produce an oxidized catalystwith reduced coke content and thereafter activating said catalyst bycontacting said oxidized catalyst with activating gas at 400 to 600 C.for a time sufficient to activate said catalyst, and thereafterreturning said catalyst to contact with stilbene and ethylene forfurther reverse disproportionation of stilbene and ethylene intostyrene.

DETAILED DESCRIPTION The Reverse Disporportionation Reaction

The total reaction of this invention may be represented by the followingequation:

    C.sub.6 H.sub.5 CH═CHC.sub.6 H.sub.5 +CH.sub.2 ═CH.sub.2 ⃡2 C.sub.6 H.sub.5 CH═CH.sub.2

Catalyst

The catalyst may contain from 0.1 to 10 wt % W, preferably 1 to 6 wt %,and 0.003 to 4 wt % Sb, preferably 0.1 to 1.5 wt %. The catalyst alsohas 0.01 to 2%, preferably 0.03 to 0.2 wt % alkali or alkaline earthmetal ion, preferably potassium. Other promoters may be present.

The support is preferably silica gel, but any other support used forconventional disproportionation catalysts may also be used though thecatalyst performance may change some.

Activation

Activation is necessary to achieve the catalyst's full potential.Activation is a partial reduction of the catalytic components, which areoxides because of the calcination step used in catalyst manufacture, orbecause of the oxidizing atmosphere used to burn off coke on spentcatalyst. Conventional activation procedures, such as used forconventional disproportionation catalysts may be used.

Reaction Conditions

The reverse disproportionation reaction conditions are given in U.S.Pat. No. 3,965,206, the teachings of which are incorporated byreference. In general, temperatures of 300 to 600 C. are adequate.Pressures from subatmospheric to 1000 atm, absolute are suitable, butoperation at 1 to 10 atmospheres gives good results.

Hydrogen or nitrogen or inerts may be present during thedisproportionation reaction. Adding hydrogen may or may not cut down oncatalyst coking, but may overreduce the catalyst. Nitrogen, and hydrogenand other inert gases, will also cut down residence time of reactants inthe reactors, if desired. I prefer to operate with reactants as the solefeed to the reactor.

The feed to the process of the present invention consists of relativelypure stilbene and ethylene. Other materials may be present, but polarmaterials act as catalyst poisons.

EXAMPLES Reactor

The experimental apparatus used in all examples consisted of a 0.5-inchOD stainless steel tube, 18-31 cm long. The catalyst was maintained inthe reactor as a fixed bed. Reactants flowed in a vapor phase, downflow, through the catalyst bed. The catalyst was supported on a quartzwool plug resting on an inert support. During the early phases of thestudy, 1/8-inch alundum beads were used, but experiments showed thatthis material was not inert and caused some coking. The later studieswere conducted using 1/8-inch long, quartz billets cut from 2 mm rod asa support.

Special precautions were taken to exclude oxygen from the apparatus andto keep the stilbene feed in the vapor phase. Special steam tracing,heating, and nitrogen purging of lines contacting stilbene are essentialin a pilot plant, but may not be as critical in a large scale commercialplant.

Catalyst Preparation

A series of catalysts was prepared. The basic catalyst contained 0.56 wt% WO₃ and 0.038 wt % K₂ O. The catalyst was prepared by adding 20 g of14-35 mesh Davison Grade 59 silica gel, which had been freshly calcined,to 28 ml of a solution containing 5 ml of 0.0236 N KOAc solution, 10 mlof H₂ O, and 13 ml of concentrated NH₄ OH. The silica gel was onlyminimally wetted by the 28 ml of liquid. The mixture was shaken for 30minutes, then dried overnight in a stream of air on a filter, andfinally calcined for 2 hours at 600 C. Various additives, those whichwere soluble in the alkaline solution described above, were simply addedto the alkaline solution along with the potassium and tungstencomponents. In some cases, because of solubility limitations, ammoniumhydroxide would not dissolve the additive, so in these cases a few dropsof concentrated HNO₃ was added to obtain a clear solution. In all casesthe total liquid volume of impregnating solution was 28 ml, the exactvolume was obtained by adjusting the amount of water added. In allcases, except where noted, additives were added sufficient to give anatomic ratio of tungsten:additive of 5:1. I believe the additives, theadded metallic components, were present as oxides on the catalysts,because of the calcination in air for two hours at 600 C.

When rhodium was added, a different procedure was used as no watersoluble rhodium compound was readily available. A large batch of basecatalyst (containing 0.56 wt % WO₃ and 0.038 wt % K₂ O) was made up asdescribed above. A 20.12 g portion of this catalyst was then impregnatedwith 25 ml of a methanol solution containing 0.0375 g of Rh (acac). Thisalcoholic impregnating solution was sufficient to just impart wetness tothe catalyst. After shaking for 30 minutes, drying in air, and calciningfor 2 hours at 600 C. the catalysts were ready for use.

Table I shows a listing of catalysts prepared.

                                      TABLE I                                     __________________________________________________________________________         Compound   Wt. of                                                        Additive                                                                           Used       Compound.sup.a, g.                                                                    Comments                                              __________________________________________________________________________    Pt   Pt(NH.sub.3).sub.2 (ONO).sub.2                                                           0.0330.sup.b                                                  Pd   Pd(NH.sub.3).sub.2 (ONO).sub.2                                                           0.0232  5 drops HNO.sub.3, boiled to dissolve salts           Ni   Ni(NO.sub.3).sub.3.6H.sub.2 O                                                            0.0281  No NH.sub.4 OH                                        Zn   Zn(OAc).sub.2.2H.sub.2 O                                                                 0.0212  No NH.sub.4 OH; 5 drops 30% H.sub.2 O.sub.2           Cr   Cr(NO.sub.3).sub.3.9H.sub.2 O                                                            0.0387  No NH.sub.4 OH; 5 drops 30% H.sub.2 O.sub.2           Fe   Fe(NO.sub.3).sub.3.9H.sub.2 O                                                            0.0390  No NH.sub.4 OH; 5 drops 30% H.sub.2 O.sub.2 ; 10                              drops HNO.sub.3                                       Ru   RuNO(NO.sub.3).sub.3                                                                     0.0306.sup.c                                                                          5 drops 30% H.sub.2 O.sub.2                           Mo   (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O                                            0.0171                                                        V    NH.sub.4 VO.sub.3                                                                        0.0114.sup.d                                                  Sn   SnSO.sub.4 0.0218  No NH.sub.4 OH; 10 drops conc. H.sub.2 So.sub.4,                              4 drops HNO.sub.3                                     Re   Re.sub.2 O.sub.7.3 (Dioxane)                                                             0.0362  No NH.sub.4 OH; 5 drops 30% H.sub.2 O.sub.2           Ag   AgNO.sub.3 0.0164                                                        Ce   Ce(NO.sub.3).sub.3.6H.sub.2 O                                                            0.0419  No NH.sub.4 OH                                        Eu   Eu(NO.sub.3).sub.3.6H.sub.2 O                                                            0.0431  No NH.sub.4 OH                                        As   As.sub.2 O.sub.5.nH.sub.2 O                                                              0.0127.sup.e                                                                          No Nh.sub.4 OH                                        U    UO.sub.2)C.sub.2 H.sub.3 O.sub.2).sub.2.2H.sub.2 O                                       0.0410  No NH.sub.4 OH                                        Mn   Mn(C.sub.2 H.sub.3 O.sub.2).4H.sub.2 O                                                   0.0237  No NH.sub.4 OH                                        Rh   Rh(acac)   0.0375  Alcoholic impregnation                                Sb   Sb.sub.2 H.sub.2 C.sub.8 H.sub.4 O.sub.12.3H.sub.2 O.sup.f                               0.0323  Only 2.05 ml of KOAc, No NH.sub.4 OH                                  0.0326                                                        __________________________________________________________________________     .sup.a 20 g of silica gel base                                                .sup.b 61.00% Pt                                                              .sup.c 35.87% Ru                                                              .sup.d 76.90% V.sub.2 O.sub.5                                                 .sup.e 87.65% As.sub.2 O.sub.5                                                .sup.f tartrate                                                          

Catalyst Activation

Catalysts were activated, in situ, by passing 200 scc/min of 60 CO overthe catalyst at a specified temperature for specified time. It ispossible to use other activating gases, or no gas at all, but a COactivation procedure was chosen as a standard one to permit screening ofthe effects of various additives on catalyst activation.

Test Procedure

The activated catalyst was then tested for its activity on a standardfeed consisting of 200 scc/min ethylene and 40 scc/min of stilbene. Theresidence time in the catalyst bed was 0.3 seconds. The products wereanalyzed by gas chromatography.

After the catalyst lost activity, it was regenerated by contacting itwith 48 scc/min of air for 45 minutes at 575 C.

A typical operating sequence is presented below:

A. Activation Cycle

1. 25 min. Nitrogen purge of lines and reactor system (200 cc/min).Ethylene purge of line up to oxygen trap. Reactor temperatureequilibrated to activation temperature.

2. 5 min. Nitrogen purge continuing. Ethylene purge of lines throughoxygen trap to vent, located at ethylene-to-saturator feed valve. COflow to vent to purge CO line in panel control board.

3. 55 min., typical. Nitrogen off. CO feed to reactor for activation,feed rate typically 200 cc/min. Ethylene purge to vent continuing, withoxygen meter (Teledyne Trace Oxygen Analyzer Model 311-1) connected tovent to monitor ethylene quality.

4. 5 min. Nitrogen purge to vent to clear lines in control panel. COfeed to reactor and ethylene feed to vent continuing.

5. 15 min. Nitrogen purge of reactor and lines. Ethylene feed to ventcontinuing. Temperature change to disproportionation run temperature.

6. 5 min. Ethylene feed to reactor, by-passing saturator. Saturator feedvalve open to reactor to equalize pressure.

B. Disproportionation Cycle

1. 30 min. Ethylene feed through stilbene saturator and thence toreactor; GC sampling program called during last 60 sec. of cycle. Stepis repeated as desired.

C. Burn-off Cycle

1. 5 min. Nitrogen purged to vent to clear lines in control panel.Ethylene feed to saturator off, but saturator feed valve to reactor opento equalize pressure.

2. 60 min. Nitrogen purge to reactor (48 cc/min). Temperature changed toburn-off temperature, usually 575 C. Air purged to vent to equilibratepressure in line.

3. 45 min. Air feed to reactor, 48 cc/min. GC analysis for CO₂ called.

4. 15 min. Nitrogen purge, 200 cc/min, through reactor system.

5. Shut down or recycle.

This procedure was used to test the different catalyst formulations.Experimental results are shown as productivity, measured as moles ofstyrene per liter of catalyst per hour. 34 moles per liter per hourrepresents about 83% conversion of stilbene to styrene. Productivity isreported both for the start of run conditions (initial) and at the endof the run, i.e., after 4.5 hours of operation (final). The data arepresented below in Table IIA.

                  TABLE IIA                                                       ______________________________________                                        EFFECT OF ADDITIVES ON CATALYST ACTIVATION                                                Activation                                                        Cata1yst.sup.a                                                                            Conditions     Productivity.sup.b                                 Additive    Time   Temp.       Initial                                                                             Final                                    ______________________________________                                        None (STD)  None           4.19    6.74                                                   1 hr   450         8.05  12.65                                                8 hr   450         27.65 19.43                                    Ce          1 hr   450         8.13  12.30                                    Eu          None           4.01    6.27                                                 1 hr 450         6.91    12.57                                      As          None           2.16    3.99                                                   1 hr   450         8.62  12.91                                                1 hr   450         8.92  13.31                                    Fe          1 hr   450         9.07  17.79                                    Cr          1 hr   450         7.10  12.20                                    Ni          1 hr   450         7.51  13.82 - Ru 1 hr 450 4.68 11.19           Pt          1 hr   450         9.38.sup.c                                                                          7.21.sup.c                               Pd          1 hr   450         7.29.sup.c                                                                          6.35.sup.c                               ______________________________________                                         .sup.a A11 additives at 5:1 W:additive mole ratio un1ess otherwise noted.     .sup.b All runs were for 4.5 hr. Run temp., 425 C.                            .sup.c Average for 2 runs.                                               

The test apparatus was then partially dismantled and rebuilt. A numberof additional tests were then run. The main difference betweenoperations reported in Table IIA and Table IIB, presented hereafter, isthe amount of oxygen contamination. I believe that the data presented inIIA reflect less oxygen contamination than those in Table IIB. Since thetesting occurred under superatmospheric pressure, about 3 psig or 1.2atm, absolute, it was thought that there could be no air contaminationdue to leaks in the piping. Reactants might leak out, but air would notget in. Several ppm oxygen diffused into the test apparatus through aleak to increase the oxygen level, and decrease the catalyst activity.Oxygen is a catalyst poison. The amount of O₂ contamination wasrelatively constant during the IIA testing period, I estimate about 0.2ppm O₂ by volume. For the IIB testing period about 0.3 ppm O₂ by volumewas present. I checked the activity of my standard, or reference,catalyst periodically during the IIA and IIB testing periods. Thestandard, or reference, catalyst consistently gave lower productivityduring the IIB tests. The results of the more O₂ contaminated runs arereported in Table IIB.

                  TABLE IIB                                                       ______________________________________                                        EFFECT OF ADDITIVES ON CATALYST ACTIVATION                                                Activation                                                        Catalyst.sup.a                                                                            Conditions     Productivity                                       Additive    Time   Temp.       Initial                                                                             Final                                    ______________________________________                                        None (STD)  1 hr   450         6.09  11.04                                                1 hr   450         5.87  11.49                                                1 hr   450         4.53  9.63                                     Rh          1 hr   450         9.82  10.60                                                1 hr   450         2.98  8.16                                                 1 hr   450         2.41  7.45                                                 8 hr   450         2.76  6.53                                     Mo          1 hr   450         3.92  7.75                                                 1 hr   450         4.75  7.56                                     V           1 hr   450         1.05  2.86                                     Sn          1 hr   450         0.04  (0.18)                                               1 hr   450         1.34  (1.61)                                   Re          1 hr   450         4.49  4.26                                     Zn          1 hr   450         2.82  4.32                                     Ag          1 hr   450         3.42  8.02                                                 1 hr   450         4.32  8.48                                     U           1 hr   450         4.98  5.47                                     Mn          1 hr   450         3.76  4.04                                     Sb          1 hr   450         10.07 9.28                                     ______________________________________                                         .sup.a A11 additives at 5:1 W:additive mo1e ratio unless otherwise noted.

It is believed that results can be compared very well within Table IIA,or within Table IIB. Direct comparison of an additive listed in TableIIB with an additive from the Table IIA is harder to make, because ofthe increased oxygen contamination in those runs presented in Table IIB.It is believed that the relative activities, i.e., activity of acatalyst in Table IIB with an additive compared to activity of acatalyst with no additives from Table IIB can be compared. These datarelative activation, for initial activity, are reported in Table III.The relative initial activities are probably more significant thanrelative end of run activities, so comparisons were made based onrelative initial activities.

                  TABLE III                                                       ______________________________________                                        Additive           Relative Activities                                        ______________________________________                                        Sb                 2.08                                                       Fe                 1.13                                                       As                 1.10                                                       Pt                 1.09                                                       Ce                 1.01                                                       Rh                 1.10, 0.56, 0.45                                           U                  1.03                                                       None (Standard)    1.00                                                       Re                 0.93                                                       Ag                 0.89, 0.71                                                 Mo                 0.89, 0.74                                                 Ni                 0.93, 0.77                                                 Cr                 0.88                                                       Eu                 0.86                                                       Pd                 0.85                                                       Mn                 0.78                                                       Zn                 0.58                                                       Ru                 0.58                                                       Sn                 0.31                                                       V                  0.16, 0.17, 0.20, 0.20                                     ______________________________________                                    

Repeated tests showing declining activities meant that a catalyst couldnot be regenerated, but lost some activity with each cycle. A singlenumber, e.g., Sb's relative activity of 2.08 meant that essentially allactivity was restored after coke burn-off, and activation. The Rhcatalyst lost activity after coke burn-off and activation.

From these data, it is apparent that a reverse disproportionationcatalyst of tungsten and potassium containing relatively small amountsof antimony gives excellent results. Activation is necessary to achievefull productivity possessed by this catalyst.

I know a one-to-five ratio of antimony: tungsten gives good results. Ibelieve that good results can be obtained with Sb:W atom ratios of 1:20to 2:1 and preferably 1:10 to 1:3. The effects of Sb are not nearly aspronounced when a more severe activation step is used. A series of testswith 575 C. activation for 1 hour gave Sb:W:K catalysts with about 10%greater initial productivity, but about 25% less final productivity ascompared to a W:K catalyst.

If I were designing a commercial plant today, I would conduct furtherexperiments to see if the various catalytic components could beoptimized further. I would probably use a catalyst containing 2 to 10times as much metal content as those catalysts used in the experiments.Commercially, you want more active catalysts, and smaller reactionvessels, and would use catalysts with a higher metal loading. I usedvery lightly loaded catalysts for my experiments because the catalystwas extremely active. "Full strength" catalyst established equilibriumconditions so rapidly that I could not discern relatively smallerdifferences caused by different additives. Based on other experimentalwork, metal loadings ten times as high can probably be achieved usingsimilar impregnation procedures, with five or tenfold increase inactivity. Phrased another way, the reactants see the active metals, notthe support, and the amount of conversion per gram of catalyticcomponents (excluding support) is roughly constant. More metal on thesupport should improve the catalyst resistance to trace amounts of O₂and polars.

I would like to learn more about the active form of the catalysts Itested. The active form may be a simple oxide or may be a mixedheteropolyacid of SiO₂, WO₃ and MO_(x), where M is the additive metal.It is possible that the oxides mentioned and claimed do not exist asdiscrete oxides, but instead form some complex polymeric structure.

I would operate a commercial plant with whatever oxygen strippingcolumns or oxygen and water absorbers were necessary to ensure oxygen,and other contaminants, especially polar ones, were excluded from theplant.

My catalyst can be disposed within the reactor as a fixed bed, fluidizedbed, moving bed, ebullated bed, or any other reactor configuration. Theadvantage of the fluidized, moving and ebullating bed reactors is thatcatalyst addition and withdrawal can be performed continuously. Thus,coke, or carbon deposition on the catalyst can be burned off, thecatalyst activated, and returned to the reactor without shutting downthe reactor. The disadvantage of this mode of operation is that thereactor designs are fairly complicated, as compared to simple fixed bed,down flow design. When fixed bed reactors are used, preferably, two orthree reactors are provided in parallel, permitting one or more reactorsto be taken off stream for carbon burn-off and activation while theother reactor(s) remain on stream.

What is claimed is:
 1. A catalyst comprising catalytically-effectiveamounts of antimony, tungsten and an alkali or alkaline earth componenton a carrier material.
 2. Catalyst of claim 1 wherein the carriermaterial is silica gel.
 3. Catalyst of claim 1 wherein the alkali oralkaline earth component is potassium.
 4. Catalyst of claim 1 whereinthe catalyst contains 0.1 to 10 wt % W, 0.01 to 2 wt % alkali oralkaline earth component and 0.03 to 4 wt % Sb, and the carrier materialis silica gel.
 5. Catalyst of claim 1 wherein the catalyst contains 1 to6 wt % W as WO₃, 0.1 to 1.5 wt % Sb as Sb₂ O₃, and 0.03 to 0.2 wt % K asK₂ O, and the carrier material is silica gel.
 6. Catalyst of claim 1wherein the Sb:W atomic ratio is 1:20 to 2:1.
 7. Catalyst of claim 1wherein the Sb:W atomic ratio is 1:5.